Bird Flu is Back

Bird flu is causing rising numbers of infections in chickens and cattle, and small numbers of mild infections in humans. California poultry flocks have once again been decimated by bird flu, with over 1.5 million chickens and turkeys culled this year.

The most prevalent bird flu strain in the US, H5N1, has killed 21 people worldwide since 2020.  However, confirmed cases of person-to-person transmission are extremely rare, even though only 1 or 2 genetic mutations in the H5 influenza gene are needed to make the virus more infectious for humans.

A recent News article in Nature (Oct. 28, 2025) reported that another bird flu strain, H9N2, has acquired to ability to infect humans. This strain is common in China, but less common elsewhere. So far, detection of infection by H9N2 in humans has been rare, although asymptomatic infections may well have been missed. Also, screening for H5N1 infection is common, but screening for H9N2 is uncommon. H9N2 bird flu can infect human cells in tissue culture, but more mutations may be required for efficient human-to-human transmission.

Why mention bird flu risks for Del Mar residents? Two important reasons: 1) high incidence of H5N1 bird flu in wild birds, poultry flocks, and cattle in California; 2) reduced surveillance and slowing of the development of bird flu vaccines under the current administration’s actions. If a bird flu pandemic emerges, we are woefully unprepared.

What can we do? Here are some tips from infectious disease experts (excerpted from Medscape Medical News, Nov. 11, 2025):

• Doctors should ask patients with flu-like symptoms about animal and dietary exposures.
• Those at risk for animal exposure should wear protective gear and practice good hygiene. This includes those with chickens in Del Mar.
• Consumption of unpasteurized milk or cheese and undercooked eggs and poultry should be avoided.
• Domestic cats are highly susceptible to bird flu, either from eating an infected bird or from exposure to raw dairy. Another potential exposure is handling bird feeders because wild birds shed the virus in their feces.
• Seasonal flu vaccination is highly recommended to reduce the risk for viral reassortment because of dual infection with seasonal and bird flu strains.